Rotating regenerators are employed also with automobile gas turbine engines to improve fuel economy. A typical regenerator comprises a cylindrical matrix rotatable about its major axis and having a multiple of axially extending gas flow passages which are alternately indexed with two separate gas streams comprising comparatively low pressure hot exhaust gas and comparatively high pressure cool inlet air. The matrix is thus alternately heated and cooled, thereby to cool the exhaust gas before it is discharged to the atmosphere and to preheat the inlet gas or air prior to its entry into the combustion chamber. Non-rotatable seals which may comprise (1) a rubbing seal in sliding sealing engagement with an axial end surface of the regenerator and (2) a static seal between the rubbing seal and a fixed portion of the regenerator housing, define a boundary between said gas streams to limit leakage from the cooler high pressure inlet air to the hot lower pressure exhaust gas. Without such seals, a large proportion of the inlet air will bypass the regenerator and escape with the exhaust, resulting in poor economy, inefficient operation of the turbine engine, and difficult engine starting.
The regenerator rotating relative to the fixed housing must necessarily have sufficient clearance to allow for thermally induced relative movement between the regenerator and housing. Accordingly the static seal must have some capability for movement without excessive stress, must have sufficient strength during high temperature operation to withstand the pressure loads across it, and must conform to both the rubbing seal and housing to limit air leakage as the parts warp thermally. In addition the static seal must be inexpensive and sufficiently compact to fit in the limited space available.
Some seals known to the art perform fairly well in accomplishing the above requirements, but such seals are expensive and sensitive to dimensional tolerance, such that localized stress is often objectionable. An important object of the present invention is accordingly to provide an improved and comparatively low cost static seal that achieves the above requirements and also improves the operation of the rubbing seal, although it is generally independent of the specific rubbing seal construction.
In order to minimize wear and especially localized wear between the rubbing seal and regenerator surface and to reduce friction force tending to oppose rotation of the regenerator, a reasonably low and uniform clamping force between the regenerator and rubbing seal is desired. In a typical construction, the pressure force across the seal amounts to fifty to seventy-five pounds per square inch. Various devices are employed to partially counter-balance the pressure force exerted against the axially outer area of the rubbing seal remote from the regenerator, including devices to apply a counter-balancing pressure force over preselected axially inner areas of the rubbing seal proximate the regenerator. However, the means for providing counter-balancing pressures at opposite sides of the rubbing seal must be relatively free from the effects of thermal distortion of dimensional tolerances in order to maintain the desired uniform low pressure induced clamping load on the rubbing seal during changing engine operating conditions. Such has not been the case heretofore in gas turbine engines of the type with which the present invention is concerned.
The present invention therefore provides as another object a static seal that enables the aforesaid desired clamping load or force and is less sensitive to dimensional variations resulting from thermal distortion and production tolerances.
Another and more specific object of this invention is to provide, in combustion with a rubbing seal having its inner surface in sliding sealing engagement with an axial end surface of the regenerator, a static seal having separate portions in sliding sealing engagement respectively with the outer surface of the rubbing seal and with a non-rotatable portion of the regenerator housing. One of the members comprising the rubbing seal and housing portion provides an integral movement limiting stop in said sliding sealing engagement with the static seal and arranged to limit pressure induced movement thereof toward the low pressure side of the seal, thereby to locate the static seal accurately when under operating pressure.
In a preferred construction the static seal is channel shaped with its channel mouth in communication with the high pressure side of the seal and with its opposite channel sides in the aforesaid sliding sealing engagements. The movement limiting stop comprises the sidewall of an axially outwardly opening seal retaining groove extending linearly of the seal and having one of the channel sides of the static seal confined therein. The retaining groove is sufficiently deep axially to accommodate operationally induced relative axial movement between said one channel side therein and the aforesaid sidewall of the retaining groove without allowing the channel side to bottom within the retaining groove or to move completely out of the latter. During operation, the sealing engagement between the various sliding parts is maintained by the pressure differential across the seal.
Another object is to provide such a seal having resilient means confined between the bottom of the seal retaining groove and the channel of the static seal. The resilient means is under compression urging the rubbing and static seals to their operating positions in said sliding sealing engagements even when the turbine engine is not operating. Thus the efficiency of the seal during engine starting condition is increased and engine starting is facilitated.
Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.